Conventionally, in the internal-defect inspection of a hollow fiber porous membrane, a visual inspection cannot be performed because the shape of the hollow fiber porous membrane is cylindrical and opaque, and therefore, a destructive inspection method has been used, wherein an internal pressure is applied to destruct the hollow fiber porous membrane. The destructive inspection can be performed by pressurizing a hollow portion from both ends of a continuous single fiber. Since the hollow portion is usually pressurized after a hollow fiber membrane module is formed, the inspection is performed in the units of module products and therefore the loss due to a defect increases, causing a decrease in the yield.
On the other hand, Patent Document 1 has proposed an on-line inspection method of a hollow fiber membrane using transmitted light. However, the technique of Patent Document 1 is a technique for eliminating the effect of direct light by using a polarizing filter, and detecting an un-whitening defect with regard to the light passing through a hollow fiber porous membrane on the opposite side of an irradiation plate. This technique can shield the neither scattered light nor transmitted light at an edge portion of a cylindrical hollow fiber porous membrane and therefore cannot be adapted for the inspection of an internal defect causing a pinhole of a target hollow fiber porous membrane.
Patent Document JP-A-9-152323